This invention relates to reproducing apparatus, and more particularly, to apparatus for generating patterns from information stored in a computer or similar storage apparatus.
The copending application of Firtion et al. Ser. No. 496,150, filed Aug. 9, 1974, and assigned to Bell Telephone Laboratories, Incorporated, describes a pattern generating machine comprising a modulated laser writing beam which scans a substrate to form a pattern by laser machining. As described in that case, laser machining of an iron oxide film is an effective way for forming the detailed patterns required in the production of integrated circuit masks. The writing beam is reflected from a mirror mounted on a carriage that reciprocates by rebounding between two displaced coil springs to give the required x-direction scanning. The substrate is stepped in a y direction after each scan by the laser writing beam. The laser writing beam is modulated by digital information; that is, by a train of stored electrical pulses each representing successive overlapping spots forming a scan line. A coding laser beam is reflected from the carriage through a stationary code plate having alternate transparent and opaque stripes to generate a code signal used to monitor the position of the carriage and to control the modulation of the writing beam.
Since efficiency and economy are prime goals in semiconductor device manufacture, it would clearly be desirable to increase the speed with which a complex mask pattern can be generated. However, because scanning speed depends on the physical velocity of the carriage as it rebounds between oppositely disposed springs, the rate of pattern generation is inherently limited. As a practical matter, pulses or spots can be laser machined at a rate of about 100 kilohertz, and it takes about 40 minutes to generate a typical complex mask pattern.